Refrigerating system



Jan. 25, 1938. H. F. BRIGGEMAN ET AL 2,105,591

REFRIGERATING SYWSTEM Filed Feb. 19, 1935 WO TEMP. VALVE.

lrwerwtos: Harold T- Bruggeman, Dger AFUHGT] Attorrwe y Patented `an.25, 1938 REFRIGERATING SYSTEM Harold F. Briggeman and Roger A. Fuller,Fort Wayne, Ind., assignors to General Electric Company, a corporationof New York Application February 19,1935, serial No. 7,210

13 Claims.

Ourinvention relates to refrigerating systems of the type having two ormore evaporators supplied with a refrigerant from a single source.

It is frequently desirable to cool a. number of rooms, compartments orthe like, of varying sizes and further to maintain each of them at adierent average temperature, or to maintain rooms of various sizes atthe same average temperature. For example, in a meat market, it may bedesirable to provide apparatus for cool- 'ing a large meat storage roomlocated in the rear of the store and also apparatus to cool a relativelysmall display case located in the front part of the store. Separateevaporators of proper capacity maybe provided for the storage room andfor the display "case, the temperature of each evaporator beingregulated according to the requirements of the compartment which itcools. If all of the evaporators are supplied with a refrigerant from acommon compressor .and condenser unit or other sourceof supply, the costof the apparatus as Well as the cost of its operation will be minimized.

It is an object of our invention to provide an improved refrigeratingsystem of the type having two or more evaporators supplied with arefrigerant.from a single source, the system being adapted to maintainsaid evaporators at different average temperatures.

It is a further object of our invention to provide a refrigeratingsystem of the type having two or more evaporators of differentcapacities supplied with a refrigerant from a single source, the systembeing adapted' to maintain said evaporators at either different or thesame average temperatures.

Further objects and advantages of our invention will become apparent asthe following description proceeds and the-features of novelty whichcharacterize our invention will be'pointed out with particularity in theclaims annexed to and forming Aa part of this specification.

For a better understanding of our invention, reference may be had to theaccompanying drawing in which Fig. l is a schematic representation 'of arefrigerating system embodying our invention and Fig. 2 is a schematicrepresentation of a modied control arrangement for one of theevaporators included in the system shown in Fig. 1.

Referring to the drawing, we have shown 'in 'y Fig. 1 a refrigeratingsystem embodying our invention. This refrigerating system is providedwith a refrigerant liquefying unit including a compressor I of thereciprocating type driven byan electric motor I I through a belt I2which is connected to a pulley I3 on the motorII and a fly-wheel I4 onthe crank shaft of the compressor IIl. 'I'he refrigerant liquefying unitalso includes a water-cooled condenser I5, to which the compressedgaseous refrigerant ,passes through a conduit I6 from the compressorIl). Cooling water enters the casing of the condenser I through theinlet |5a and leaves through the outlet I5b as indicated by the arrowsin the drawing. The gaseous refrigerant is liquefied in thecondenser I5and the liquid refrigerant passes therefrom through a refrigerant supplyconduit Il. The refrigerant supply conduit I'I is provided with branchesI8 and I9 through which the liquid refrigerant is supplied to theevaporators and 2i. In this form of our invention, the evaporator 20 isa forced draft type evaporator of relatively large capacity, beingprovided with a motor driven fan 2Ilafor circulating air over thesurfaces thereof. The evaporator 20 is arranged to be maintained at arelatively high temperature as compared to the evaporator 2l. Theevaporator 20 may be used to cool a storage chamber, for example, andthe smaller evaporator 2I may be used to cool a display case. Theevaporator 2| is of the fin type, air being circulated over its surfacesby natural convection.

An automatic thermostatic expansion valve 22 is provided in the inlet ofthe evaporator 2li and controls the admission of liquid refrigerantthereto by throttling the same. The automatic thermostatic expansionvalve 22 is of the conventional type, and includes a bulb 23 connectedthereto by conduit 24, the bulb 23 containing a uid such as sulphurdioxide, which is cooled by the portion of. the evaporator 20 adjacentthe outlet thereof. A bellows or similar pressure responsive member isincluded in the thermostatic expansion valve 22, and is subjected to thepressure of the refrigerant in the evaporator 20. When the pressuredecreases the bellows lor the like opens the valve to admit refrigerantto the evaporator 20, and as the pressure increases the bellows or thelike gradually closes valve 22, thus cutting off the supply of liquidrefrigerant to the evaporator 20. The thermostatic expansion valve 22 isso arranged that on a rise in temperature at the outlet of theevaporator 20 the expansion of the fluid in the bulb 23 causes the valve22 to open and conversely on a drop in this temperature the fluidcontractsand causes the valve to close. Since for every refrigerantvapor pressure in the evaporator there is a corresponding temperature,it will be seen that the valve 22 is controlled by the differencebetween the temperature in the evaporator 20 and the ternperature of thebulb 23, and in consequence maintains this diiference at a constantvalue. Maintaining this difference in temperature really amounts tocontrolling the superheat of the gas at the outlet of the evaporator,that is, the warming of the refrigerant Vapor above the temperature atwhich it is vaporized. "It is necessary to maintain this superheatconstant in order that no liquid refrigerant will pass to the compressorl0, so as to protect the latter and to maintain eicient operation of thesystem.

A two-temperature valve 25 of the conventional pressure operatedsnap-acting type is provided at the outlet of the evaporator 20., Thevalve 25 is arranged to close the outlet of the evaporator 20 when thepressure therein reaches a predetermined low value and to open againwhen the pressure in the evaporator 20 reaches a predetermined highervalue. The two-temperature valve 25 thus serves to maintain theevaporator 20 within the limits of the above mentioned predeterminedtemperatures. Vaporized refrigerant passing through the two-temperaturevalve 25 enters a suction conduit 26, passes therethrough to the mainsuction conduit 21 through which it -returns to the intake of thecompressor l0. It

will thus be seen by the use of the two-temperature valve 25, we haveprovided an arrangement by which the evaporator 20 may be maintained ata relatively high temperature, while at the same time -all of thecooling surfaces of the evaporator 20 may be utilized. It is thusunnecessary to starve the evaporator in order to maintain it atarelatively high temperature, that is, it is unnecessary underconditions of light load on the evaporator 20 to limit the refrigerantsupplied thereto to such an amount that only a part of the surface ofthis evaporator is utilized for cooling.

In the preferred form of our invention, in which the evaporator 20 isused to cool a storage room or the like, the two-temperature valve 25 isset to open at a temperature above 32 F. and to close at a temperaturebelow 32 F. The pressure settings might be 12 lbs. per square inch and 0lbs. per square inch gauge pressure, for example, if SO2 is used as therefrigerant. The evaporator .20 is thus operated alternately above andbelow 32, that is, on what is known as a defrosting cycle, Suchoperation isadvantageous in that the relative humidity of the air in theroom or space cooled by the evaporator 20 is increased and thedehydration of articles preserved therein is decreased.

The low temperature evaporator 2| is provided with an automaticthermostatic expansion valve 28 at the inlet thereof, which is similarto the automatic thermostatic expansion valve 22 described above. Thethermostatic expansion valve 28 includes a bulb 29 connected thereto bya. conduit 30, the fluid in the bulb and conduits 29 and 3|) beingcooled by a portion of the evaporator 2| adjacent the outlet thereof soas to maintain substantially constant the superheat of the vaporizedrefrigerant withdrawn from the evaporator. In order to maintain theillustrative conditions high and low temperatures of the evaporators 20and 2| noted above, it is necessary to provide some control arrangementfor maintaining the temper-ature of the evaporator 2| at a relativelylower value than the temperature of the evaporator 20. If atwo-temperature valve, similar to the valve 25, were placed in theoutlet of the evaporator 2|,

however, diculties under certain conditions of operation would arise.For example, if the evaporator 20 were subjected to a sudden heavy loadas by the placing of a large quantity of material to be cooled inproximity thereto, the pressure in the evaporator 20 would remain for along period of time at a value too high to cause closing of the Valve25, and the compressor I0 would continue to operate during all thisperiod. At the same time, if such a two-temperature valve were arrangedat the outlet of the evaporator 2| the valve would remain open, as itwould be set for a lower value of pressure for closing. During a longperiod of the time mentioned, the evaporator 2| would be subjected to alow suction pressure and the compartment cooled by the evaporator 2|would thus be subjected to sustained -low temperature for too longaperiocl. In order to overcome this diiculty, we have provided a valve3| located in the supply conduit of the evaporator 2| in series with thethermostatic expansion valve 23. The valve 3| is of the shut-oil` type,that is, it moves from the fully open to the fully closed position asdistinguished from the gradual opening of' the valve 28, for example,with its consequent throttling action. The valve 3| is opened by asolenoid l32 which is energized by current supplied through theconductor 33. The electric circuit through the conductor 33 is openedand closed by a thermostatic operating mechanism 34 which includes afluid containing bulb 35 connected thereto by a conduit 36. The bulb 35is responsive to the temperature of the evaporator 2| and in theillustrative form of ourinvention is located on the surface thereofadjacent its center. When the evaporator 2| reaches a predetermined hightemperature, the fluid in the bulb 35 and the conduit 36 expands, as itis warmed by the evaporator 2|, and actuates a bar 31a to close contacts31 of the thermostatic switching device 34, thus completing theoperating circuit of the solenoid 32. When the s'olenoid 32 is thusenergized, it opens the valve 3| and admits the liquid refrigerant tothe evaporator 2|. This liquid refrigerant vaporizes inthe evaporator 2|and when the latter, as a consequence, reaches a. predetermined lowtemperature, the contraction of the iiuid in the bulb 35 and conduit 36causes the contacts 31 to open, thus de-energizing the solenoid 32. Upona deenergization of the solenoid 32, the valve 3| is closed by a spring32a and the supply of liquid refrigerant to the evaporator 2| isstopped. y After the. vaporization of the liquid refrigerant remainingin the evaporator l2|, the temperature of the latter will rise until itagain reaches the predetermined temperature at which the contacts 31 areclosed and the cycle repeated. In the illustrative form of our inventionthe valve 3| might be setto open and close at 36 F. and 22 F.respectively. When the evaporators 20 and 2| are subjected to stableload conditions, the solenoid operated valve 3| functions primarily as aprotective device rather than as a control device.

The refrigerant vaporized in the evaporator 2| passes therefrom througha suction conduit 38 to the common suction conduit 21 through which itreturns to the intake of the compressor I0. A'

check valve 39 is provided in the suction conduit 38 in order to preventvaporized refrigerant from the evaporator 20 entering the evaporator 2|when the latter has been exhausted to a low pressure. i

A back pressure control device 40 has been provided in the' suctionconduit 21 for controlling the motor Il. The back pressure controldevice 43 includes a diaphragm 4| which is subjected to the pressureexisting in the suction conduit 21 through a pressure connection 42 andis biased by a compression spring 43. When the pressure in the suctionconduit 21 reaches a predetermined high value, the 4diaphragm 4| ismoved upwardly against the bias of the spring 43, thus moving thecontact 44 into engagement with the stationary contact 45 and completingthe supply circuit of the electric motor through the conductors 46. Theelectric motor is thus started and it drives the compressor I3 until thepressure in the suction conduit 21 reaches a predetermined low value inconsequence of which the diaphragm 4| moves downwardly carrying themovable contact 44 therewith, thus opening the elecpressure controldevice 43 more nearly in accord-A ance with the requirementsof thecolder evaporator 2|, since if the compressor |3 reduces the pressure inthe suction line 21 below the point for which valve 25 is set the latterwill close while the refrigeration of the evaporator 2| may continue. Ifthe valve 3| is arranged to open and close at 36 F. and 22 F.;respectively, the control device 43 may be set to open and close at l0'lb. pressure and 6 in. vacuum respectively.

It will be understood that the various valve settings may be altered inorder to provide for `desired temperatures of the evaporators asrequired ,in various applications. The valves 22, 25, 23 and 3| may beset to maintain the evaporators 23 and 2| within the same temperaturerange despite their different capacities if such operation is desired.

In Fig. 2 of the drawing, we have shown a modified control arrangementfor an evaporator 53, which corresponds to the evaporator 2| in thesystem shown in Fig. 1. The evaporator 53 is of the iin type and is ofrelatively vsmall capacity as compared'to the evaporator 23. Liquidrefrigerant is supplied to the evaporator 53 through a conduit 5|, theadmission of liquid refrigerant to the evaporator 53 being controlled bya thermostatic expansion valve 52. A'I'he valve 52 is similar to thevalve 23 described above and is provided with a bulb 53 connectedthereto by a conduit 54, the bulb 53 being located at the outlet of theevaporator 53, so as to maintain substantially constant the superheat ofvapor withdrawn from this evaporator. AA shut on valve 55 is provided ina suction line 53 in order 'to control the ow of refrigerant through theevaporator 53, and thus maintain the same within a predetermined rangeof relatively low temperatures.` The valve 55 is opened by a solenoid51, which is energized by current supplied through a conductor 53. Theelectric circuit through the conductor 53 is opened and closed by athermostatic operating mechanism 53, which includes a duid containingbulb 33 connected thereto by a conduit 6|. 'I'he bulb 53 is responsiveto the temperature of the evaporator 53 and in the form of our inventionillus'- trated is located on the surface thereof adjacent its center.When the evaporator 53 reaches a predetermined high temperature, the uidin the bulb 33 and the conduit' 3| expands as it is warmed by theevaporator 53 and closes contacts 32 of the thermostatic switchingdevice 53 by a bar 53, thus completing the operatingcircuit of thesolenoid 51. When the solenoid'51 isthus energized, it opens the valve55 against the action of a spring 55a, thus permitting the flow ofrefrigerant through the evaporator 53 to the suction line 53. 'I'heremainder of the refrigerating system for use with 'the modified controlarrangement shown in Fig. 2 is the same as that shown in Fig. 1.

While we have shown a particular embodiment of our invention inconnection with a compression refrigerating machine, we do not desireour invention to be limited to the particular construction shown anddescribed, and we intend in the appended claims to cover allmodifications within the spirit and scope of our invention. v

What we claim as lnew and desire to secure by Letters Patent oftheUnited States is: i.

l. A refrigerating system having a plurality of refrigerant evaporators,each of said evaporators having a refrigerant outlet, means including arefrigerant liquefying unit yfor supplying liquid refrigerant tosaidevaporators, conduits connecting the outlets of said evaporators tosaid liquefying unit in parallel relationship, control means responsiveto the refrigerant pressure prevailing at the outlet of one of saidevaporators and including a valve at the outlet of said one of saidevaporators for maintaining the temperature thereof within apredetermined range of relatively high tem'peratures, means including asolenoid operated shut oi valve located in the conduit connecting. theoutlet of another of .said

Aevaporators to said refrigerant liquefying unit for shutting off theflow of refrigerant therethrough,

and means for controlling said solenoid to control said shut o valve inaccordance 'with the temperature produced by said last mentionedevaporator and for maintaining the temperature thereof within apredetermined range of relatively low temperatures, said second namedcontrol means being independent of said first named control means.

2. A refrigerating system having a plurality of` refrigerantevaporators, each of said evaporators having a refrigerant inlet andoutlet, means including a refrigerant liquefying unit for supplyingliquid refrigerant to said evaporators, supply and exhaust conduitsconnecting the inlets and outlets of said evaporators to said liquefyingunit in parallel relationship, means including a thermostatic expansionvalve responsive to the temperature at the outlet of one of saidevaporators and located at the inlet thereof for throttling the flow Vofrefrigerant therethrough, control means renoid operated stop valvelocated in the exhaustconduit of the .last mentioned evaporator forlshutting oil' the ow of refrigerant therethrough,

and means for controlling said solenoid to control said shut oil valvein accordance with the temperature produced by said la'st mentionedevaporator and for maintaining the temperature thereof within apredetermined range of relatively low temperatures, said second namedcontrol means being independent of said i'lrst named control means.

3. A refrigerating system having a plurality of refrigerant evaporators,each of said evaporators having a refrigerant inlet and outlet, meansincluding a compressor and supply conduits for supplying liquidrefrigerant to said evaporators, a common suction conduit connecting theoutlets of said evaporators to said compressor in parallel relationship,means responsive to the pressure in said common suction conduit forstarting said compressor at a. predetermined maximum pressure andstopping said compressor at a predetermined minimum pressure, meansincluding a thermostatic expansion valve responsive to the temperatureat the outlet of one of said evaporators and located at the inletthereof for throttling the flow of refrigerant therethrough, controlmeans responsive to the refrigerant pressure prevailing at the outlet ofone of said evaporators and including a two-temperature stop valve atthe outlet of said one evaporator for maintaining the temperaturethereof within a predetermined range of relatively high temperatures,means including a second thermostatic expansion valve responsive to thetemperature at the outlet of another of said evaporators and located atthe inlet thereof for throttling the iiow of refrigerant therethrough,means including a solenoid operated shut off valve located in a supplyconduit of the last mentioned evaporator for shutting off the flow ofrefrigerant through said last mentioned evaporator, and means forcontrolling said solenoid to control said shut oi valve in accordancewith the temperature produced by said last mentioned evaporator and formaintaining the temperature thereof within a predetermined range ofrelatively low temperatures, said second named control means beingindependent of said first named control means.

' 4. In a refrigerating system having Va plurality of refrigerantevaporators, one of said evaporators having a relatively large capacityand another of said evaporators having a relatively small capacity, eachof, said evaporators having a refrigerant inlet and outlet, meansincluding a refrigerant liquefying unit for supplying liquid refrigerantto said evaporators, conduits connecting the outlets of said evaporatorsto said liquefying until in parallel relationship, means including anautomatic expansion valve located at the inlet of said evaporator ofrelatively large -said shut of! valve in accordance with the temcapacityfor throttling the flow of refrigerant therethrough, control meansresponsive to the refrigerant pressure prevailing at the outlet of saidevaporator of relatively large capacity and including a two-temperaturestop valve located at the outlet of said evaporator of relatively largecapacity for maintaining, the temperature thereof within a predeterminedrange of temperatures, means including a second automatic expansionvalve located at the inlet of said evaporator of relatively smallcapacity for throttling the flow of refrigerant therethrough, meansincluding a solenoid operated shutoff valve for` shutting of! the flowof refrigerant through said evaporator of relatively small capacity, andmeans for controlling said solenoid, to control perature produced by thelast mentioned evaporator and for maintaining the temperature thereofwithin said predetermined range of temperatures, said second namedlcontrol means being independent of said rst named control means.

5. A refrigerating system having a plurality of refrigerant evaporators,each of said evaporators having a refrigerant outlet, means including arefrigerant liquefying unitfor supplying liquid refrigerant to saidevaporators, conduits connecting the outlets lof said evaporators tosaid liquefying unit in parallel relationship, control means responsiveto the refrigerant pressure prevailing at the outlet of 'one of saidevaporators and including a valve at the outlet of said one of saidevaporators for maintaining the temperature thereof Within apredetermined range of relatively high temperatures, means including anexpansion valve located at the inlet of another of said evaporators forthrottling the ow of refrigerant therethrough, and a second controlmeans shutting oi the iiow of refrigerant through said last mentionedevaporator and dependent upon the temperature produced by said lastmentioned evaporator for maintaining the temperature thereof Within apredetermined range of relatively low temperatures, said second controlmeans being independent of said rst named control means.

6. A refrigerating system having a plurality of refrigerant evaporators,each of said evaporators having a refrigerant outlet, means including `arefrigerant liquefying unit for supplying refrigerant to saidevaporators, conduits connecting the outlets of said evaporators to saidliquefying unit in parallel relationship, control means responsive tothe refrigerant pressure prevailing at'the outlet of one of saidevaporators and including a valve at the outlet of. said one of saidevaporators for maintaining the temperature'thereof within apredetermined range of relatively high temperatures, means including anexpansion valve located at the inlet of another of said evaporators forthrottling the flow of refrigerant therethrough, means including asolenord operated shut off valve for shutting off the flow ofrefrigerant'through said last mentioned evaporator, and means forcontrolling said solenoid to control said shut olf valve in accordancevvith the temperature produced by said last mentioned evaporator and formaintaining the temperature thereof within a predetermined range ofrelatively loW temperatures, saidsecondnamed 4control means beingindependent of said first named control means.

7. A refrigerating system having a plurality ofrefrigerant evaporators,each of said evaporators having a refrigerant outlet and a refrigerantinlet, means including a refrigerant liquefying unit for supplyingliquid refrigerant to said evaporators, exhaust and supply conduitsconnecting the outlets and inlets of said evaporators to said liquefyingunit in parallel relationship, control means responsive totherefrigerant pressure prevailing at the outlet of one of said evaporatorsand including a valve at the outlet of said one of said evaporators formaintaining the temperature thereof within a predetermined range ofrelatively high temperatures, means including an expansion valve locatedat the inlet of another of said evaporators for throttling the flow ofrefrigerant therethrough, means including asolenoid ,operated shut offvalve located in the supply conduit of said last mentionedevaporator forshutting off the flow of liquid refrigerant therethrough, and means forcontrolling said solenoid to control said shut oif valve in accordancewith the temperature produced by said last mentioned evaporator and formaintaining the temperature thereof within a predetermined range ofrelatively low temperatures, said second named control means beingindependent of said ilrst named control means. y

8. A refrigerating system having a plurality o'f refrigerantevaporators, each of said evaporators having a refrigerant outlet, meansincluding a refrigerant liquefying unit for supplying liquid to saidevaporators, conduits connecting the outlets of said evaporators to saidliquefying unit in parallel relationship, control means responsive tothe refrigerant pressure prevailing at the outlet of one of saidevaporators and including a two-temperature stop valve located at theoutlet of said one of said evaporators for maintaining the temperaturethereof within a predetermined range of relatively high temperatures,means including an expansion valve located at the inlet of another ofsaid evaporators for throttling the flow of refrigerant therethrough,and a seicond control means shutting o the flow of re-A frigerantthrough said last mentioned evaporator and dependent upon thetemperature of said last mentioned evaporator for maintaining thetemperature thereof within a predetermined range of relatively lowtemperatures, said second control means being independent of said rstnamed control means.

9. YA refrigerating system having a plurality of refrigerantevaporators, each of said evaporators having a refrigerant outlet, meansincluding a compressor for supplying liquid refrigerant to saidevaporators, a common suction conduit connecting the outlets of saidevaporators to said compressor in parallel relationship, meansresponsive to the pressure in said common suction conduit for startingsaid compressor at a predetermined maximum pressure and for stoppingsaid compressor at a predetermined minimum pressure, control meansresponsive to the refrigerant pressure prevailing at the outlet of oneof said evaporators and including a valve at the outlet of said one ofsaid evaporators for maintaining the temperature thereof within apredetermined range of relatively high temperatures, means including anexpansion valve located at the inlet of another of said evaporators forthrottling the flow of refrigerant therethrough, and a second controlmeans shutting 0E the ilow of refrigerant through said last mentionedevaporator and dependent upon the temperature of said last mentionedevaporator for maintaining the temperature thereof within apredetermined range of relatively low temperatures, said second controlmeans being independent of said first named control means.

10. A refrigerating system having a'. plurality of refrigerantevaporators, -each of said evaporators having a-refrigerant outlet,means includving a refrigerant liquefying unit for supplying liquidrefrigerant to said evaporators, conduits connecting the outlets of saidevaporators to said liquefying unit in parallel relationship, controlmeans responsive to the refrigerant pressure prevailing at the outlet ofone of`said evaporators and including a valve at the outlet of said oneof said evaporators 'for maintaining the temperature thereof alternatelyabove and below 32 F., means including an expansion valve located at theinlet of another of said evaporators for throttling the fiow ofrefrigerant therethrough, and a second control means shutting oil? theiiow of refrigerant through said last mentioned evaporator and dependentupon the temperature of said last mentioned evaporator for maintainingthe temperature thereof within a predetermined Arange of relatively lowtemperatures, said second control means being independent of said firstnamed control means.

11. A refrigerating system having a. plurality of refrigerantevaporators, each of .said evaporators having a, refrigerant outlet,means including a refrigerant liquefying unit for supplying liquidrefrigerant to said evaporators, conduits connecting the outlets of saidevaporators to said liquefying unit in parallel relationship, controlmeansl responsive to the refrigerant pressure prevailing at the outletof one of said evaporators and including a vtwo-temperature stop valveat the outlet of said one of said evaporators for maintaining thetemperature thereof alternately above and below 32 F., means includingan expansion valve 'located at the inlet of another of said evaporatorsfor throttling the flow of refrigerant therethrough, and a secondcontrol means" shutting oif thefiow of refrigerant through said orators,conduits yconnecting the outlets of said A evaporators to saidliquefying unit in parallel re. lationship, control means responsive tothe re-v frigerant pressure prevailing at the outlet of said evaporatorof relatively large capacity andv including a valve at the outlet ofsaid evaporator of relatively large capacity for maintaining thetemperature thereof within a predetermined range of relatively hightemperatures, means including an expansion valve located at the inlet ofsaid. evaporator of relatively small capacity for throttling the flow ofrefrigerant therethrough, and a second control means shutting off the owof refrigerant through said evaporator of relatively small capacity anddependent upon the temperature produced by said last mentionedevaporator for maintaining the temperature thereof within apredetermined range of relatively low temperatures, said'second controlmeans being independent of said rst named control means.

13\. A refrigerating system having a plurality of refrigerantevaporators, one ofsaid evaporators having a relatively large capacityand another` of said evaporators having a relatively small capacity,`each of said evaporators having a refrigerant outlet, means including arefrigerant liquefying unit for supplying liquid refrigerant to saidevaporators, conduits connecting the outlets of said evaporators to saidliquefying unit in parallel relationship, .control means responsive tothe refrigerant pressure prevailing at the outlet of said evaporator ofrelatively large capacity and including a two-temperature stop valvelo'- cated at the outlet of. said evaporator of relatively largeVcapacity for maintaining the temperature thereof Within a predeterminedrange of relatively high temperatures,y means including an expansionvalve located at the inlet of said evaporator of relatively smallcapacity for throttling the flow of refrigerant therethrough, and asecond control means shutting off the ilow of refrigerant through saidevaporator of relatively small capacity and dependent upon thetemperature of said last mentioned evaporator for maintaining thetemperature thereof within a predetermined range of relatively lowtemperatures, said second control means being independent o said firstnamed control means.

HAROLD F. BRIGGEMAN. ROGER A. FULLER.

